Reversing ratchet wrenches are widely used by automobile mechanics, maintenance personnel and home craftsmen and hobbyists. These ratchet wrenches, such as those shown in U.S. Pat. No. 5,199,330 assigned to the assignee of the present invention, generally comprise a reversing pawl cooperating with a ratchet gear having an integrally-formed square cross-sectioned drive tang provided with a spring-loaded ball detent, and a selected one of a plurality of interchangeable wrench sockets is removably mounted on the drive tang and is resiliently retained thereon by the ball detent.
Under heavy-duty loads incurred during final tightening or initial loosening of a nut (or other fastener) and especially where undue leverage is exerted on the ratchet wrench, slippage in the square drive, as well as premature failure, may occur in the square cross-sectioned drive tang.
In an effort to alleviate this problem and yet provide for heavy-duty torque transmission between the drive tang and the socket, a product currently being market-introduced in Europe consists of a plurality of circumferentially-spaced radially-extending arcuately-formed lobes provided on the bottom or lower portion of an enlarged square cross-sectioned drive tang. These lobes define therebetween a plurality of recesses or pockets which cooperate with driving shoulders or lugs formed down within the driven wrench socket. Thus, these lobes are quite similar to a spline-drive socket such as that shown in the now-expired U.S. Pat. No. 3,073,192 and, in fact, the lobes (or splines) are terminated along the longitudinal axis of the drive tang, that is, they terminate intermediately of the length of the tang. Moreover, the axial length of the tang above the lobes, while being of a substantially square cross-section, has a clearance with respect to the square cross-sectioned hole in the socket. As a result, the torque is transmitted primarily through the arcuate lobes, not the square drive, thus placing heavier loading upon the lobes.
There are several major disadvantages in this construction. First, the lobes are formed out of a substantially enlarged cross-sectioned drive tang. For example, in order to provide a so-called "super" 3/8" drive, the distance between the "bottoms" of the pockets (measured across the cross-section of the tang) is 3/8". This is costly and inefficient. Second, the torque transmission is primarily between the lobes on the drive tang and the pockets in the wrench socket, in effect, a truncated spline drive and not primarily between the square drive itself. Moreover, this drive across the lobes is relatively far removed from the ratchet mechanism in the wrench (measured in a plane perpendicular to the plane or planes of the wrench) and, as a result, undue bending or torsional loads are imposed on the drive tang. Third, the tang itself is specially formed and is usable only with the specially designed sockets; thus conventional sockets cannot be used on the wrench, nor can the specially-designed sockets be used on a conventional wrench.